1) Field of the Invention
This invention relates generally to fabrication of polysilicon gates in a semiconductor device and more particularly to the in-situ etching of a bottom anti-reflective coating (BARC) layer, an oxide layer and a polysilicon layer in one high density plasma (HDP) polysilicon etcher.
2) Description of the Prior Art
Semiconductor manufacturing technology has advanced to the point where a single die may contain millions of active devices. A key requirement for fabricating such high density circuits is the elimination of contaminants from the manufacturing process. This has led to the development of ultra high vacuum processing and closed manufacturing systems. Such closed systems Preferably include insitu Process sequences that can be precisely controlled without exposure of the wafer to the ambient.
One area of semiconductor manufacture in which the elimination of contaminants and the precise control of process sequences is important is in the etching techniques for etching different film layers formed on the wafer. In general, integrated circuits are formed by patterning regions on a substrate and the by patterning layers formed on the substrate. As an example, a substrate is typically formed with an oxide layer, such as silicon dioxide. This oxide layer may function as a gate oxide to the active devices formed on the substrate. In addition this oxide layer may function as the dielectric layer for capacitors formed on the substrate. Other film layers may be formed or deposited on the gate oxide. As an example, polysilicon may be deposited on the gate oxide layer as a surface conduction layer. Other films in turn, may be deposited on the polysilicon layer. These various film layers must be patterned and etched to the gate oxide. The technique of photolithography is frequently used to pattern and etch these different film layers. Typically this involves coating the wafer with a photoresist. The photoresist is then exposed with ultraviolet radiation through a mask. A desired pattern is thus imaged on the photoresist to form a photoresist mask. The photoresist mask includes exposed areas that allow an underlying film to be etched using wet or dry etching processes. The etch depth or endpoint must be closely controlled to insure that an underlying layer (i.e. gate oxide) is not also etched through. For etching the small dry features required for high density application, Dry etch processes are typically utilized. With dry etching, gasses are the primary etch medium. Plasma dry etching uses plasma energy to drive the reaction.
As the industry moves towards higher density applications, the gate oxides used for the active devices of a semiconductor have tended to become thinner. Such thin gate oxides require etching techniques and etchants that are highly selective to the gate oxide are is then a need in the industry for better methods for patterning and etching the layers of a semiconductor structure, particularly polysilicon which have been formed on a thin gate oxide.
It is known in the industry that in a plasma dry etch process the etch selectivity to a gate oxide can be more easily achieved when there is no photoresist present during the polysilicon to gate oxide etch step. Accordingly, in a representative prior art process sequence for etching a semiconductor structure that includes a gate oxide, another oxide layer is first deposited over the semiconductor structure. A layer of photoresist in then deposited on the oxide layer. An oxide hard mask is formed to the polysilicon layer by etching the oxide layer through the photoresist mask. For stripping the photoresist, the wafer is transferred to a photoresist strip chamber. With the photoresist removed, the wafer is transferred to a poly etch chamber to etch the polysilicon layer to the gate oxide.
The transfer of the wafer during the different etch steps tends to introduce contaminants during this process. In particular, exposure of the wafers to ambient may introduce contaminates. Additionally, each different process chamber may introduce contaminants. Moreover, process parameters are difficult to control with physical transfer of the wafers between these different process stations. Finally, the operation of these different process stations is time consuming and adds to production costs.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 5,545,558(Yoo) shows a method of etching a gate by etching 1) ARC hard mask, 2) SOG and 3) poly.
U.S. Pat. No. 5,219,788(Abernathey) Bilayer metallization cap for photolithography--shows a process of patterning a conductive layer.
U.S. Pat. No. 5,346,586(Keller) Method for selectively etching polysilicon to gate oxide using an insitu ozone photoresist strip--The method is performed insitu in a plasma etch chamber.
U.S. Pat. No. 5,094,712(Becker) One chamber in-situ etch process for oxide and conductive material--shows a method to anisotropically etch an oxide/silicide/poly sandwich structure on a silicon wafer substrate in-situ, that is, using a single parallel plate plasma reactor chamber and a single inert cathode.
However, further improvements are necessary.